Geochemistry and minerals at DSDP Hole 70-504B

In three veins from the lower part of Deep Sea Drilling Project Hole 504B, 298 meters below the top of basement, primary augite is replaced by aegirine-augite. This transformation occurs only in subophitic basalts, at the contact with veins which always include a dark-olive, Mg-rich clay mineral. Talc occurs in one of these veins; it can be regarded either as a vein constituent or as a product of augite alteration. Melanite (Ca,Fe,Ti-rich garnet) appears in only one of these three veins, where a Ca-carbonate is associated with a Mg-rich clay mineral. The occurrence of melanite in Hole 504B could be due to the conjunction of particular conditions: (1) basalt with a subophitic texture, (2) presence of hydrothermal fluids carrying Ca, Fe, Si, Ti, Al, Mg, and Na, (3) rather high temperatures. Possibly the melanite and aegirine-augite formed by deuteric alteration.

Geochemistry and minerals at DSDP Hole 76-534A

Leg 76 sampled 31.5 m of basaltic basement at Deep Sea Drilling Project Hole 534A in the Blake-Bahama Basin. The basalts represent a short section of mineralogically uniform, sparsely plagioclase-phyric pillow flows, composed mainly of plagioclase, augitic clinopyroxene, iron-titanium oxides with variable amounts of alteration products (smectite ± carbonate ± quartz). Their major element chemistry is typical of mid-ocean ridge tholeiites and has normative compositions of olivine tholeiites. Mg/(Mg + Fe**2+) ratios range from 0.58 to 0.60, which suggests that these basalts are evolved compared to primitive mantle melts.

Secondary minerals and geochemistry in basalts at DSDP Leg 67 Legs

Secondary minerals in basalts from Holes 495 and 500 include smectite and chlorite, both of which have partially replaced the basalt groundmass. In addition to these two minerals, amphibole, laumontite, albite, and a corrensitelike mineral are present in Holes 499B and 499C. Smectite, chlorite, talc, calcite, phillipsite, mica, and mixed-layer chlorite-montmorillonite also fill veins in the basalts of Hole 495. The secondary mineral assemblages from Site 499 are characteristic of the initial stage of greenschist facies metamorphism.

Composition of rocks, minerals, water, and gases from uplift areas of the Central Atlantic

Original geological, geophysical, lithological, mineralogical data on uplifts of the Central Atlantic are given in the book based on materials of Cruise 1 of the R/V Akademik Nikolaj Strakhov. Geological and geophysical studies include description of the obtained material and analysis of structural and morphological elements of the ocean floor. Results of lithological, petrochemical and geochemical studies were extremely innovative and develop a conceptual model. The latter include studies of petrochemical evolution of tholeiitic alkaline plate volcanism, large-scale hydrothermal transformation of basement rocks - palygorskitization, phosphatization and ferromanganese mineralization. Showing imposition Superposition of hydrogenic alteration on hydrothermally altered rocks and its role in Cenozoic history of sedimentation is shown.

Isotopic and chemical compositions of lower crust rocks and minerals from ODP Hole 176-735B

The composition of gabbroic rocks from the drill core of Hole 735B (ODP Leg 176) at the 11 Ma Atlantis II bank close to the slow spreading Southwest Indian Ridge (SWIR) has been analyzed for major and trace elements and Sr, Nd and Pb isotopic composition. The samples are thought to represent much of the mineralogical and geochemical variation in a vertical 1-km section (500-1500 m below the sea floor) of the lower ocean crust. Primitive troctolitic gabbros, olivine gabbros and gabbros that have Mg#=84-70, Ca#>61 and low Na# (Na/(Na+Al)) (8-17) are intruded by patches or veins of more evolved FeTi-oxide rich gabbroic and dioritic rocks with Mg# to 20, Ca# to 32, Na#=14-23, TiO2<7 wt.% and FeOtotal<18 wt.%. All rocks are acdcumulates, and incompatible element concentrations are low, e.g. Pb=0.1-0.7 ppm and U

Physical properties and bulk minerals from IODP Holes 308-U1322B, U1322D and U1324B

How the micro-scale fabric of clay-rich mudstone evolves during consolidation in early burial is critical to how they are interpreted in the deeper portions of sedimentary basins. Core samples from the Integrated Ocean Drilling Program Expedition 308, Ursa Basin, Gulf of Mexico, covering seafloor to 600 meters below sea floor (mbsf) are ideal for studying the micro-scale fabric of mudstones. Mudstones of consistent composition and grain size decrease in porosity from 80% at the seafloor to 37% at 600 mbsf. Argon-ion milling produces flat surfaces to image this pore evolution over a vertical effective stress range of 0.25 (71 mbsf) to 4.05 MPa (597 mbsf). With increasing burial, pores become elongated, mean pore size decreases, and there is preferential loss of the largest pores. There is a small increase in clay mineral preferred orientation as recorded by high resolution X-ray goniometry with burial.

(Table 1) Heavy fraction minerals in bottom sediments of the Markov Deep, Mid-Atlantic Ridge

An additional ore field in the central part of the MARhas been discovered. Together with previously discovered Logachev (14°45'N) and Ashadze (12°58'N) ore fields, the new ore field constitutes a cluster with preliminarily estimated total ore reserve of >10 Mt, which is comparable with large continental massive sulfide deposits.

Secondary minerals and geochemistry at DSDP Legs 68 and 69

Basalt samples recovered during DSDP Legs 68, 69, and 70 from a 550-meter-thick section in two holes near the Costa Rica Rift (Holes 501 and 504B) were found to contain the following secondary minerals: trioctahedral and dioctahedral smectite, chlorite, mixed-layer clays, talc, hematite, pyrite, foujasite, phillipsite, analcime, natrolite, thomsonite, gyrolite, aragonite, calcite, anhydrite, chalcocite, Fe-hydrosilicate, okenite, apophyllite, actinolite, cristobalite, quartz, and magnesite. A less positive identification of bismutite was made. A mineral rich in Mn and minerals with strong reflections at 12.9 Å and 3.20 Å remain unidentified. Trioctahedral smectite replaces glass and olivine in the basalt groundmass. The other secondary minerals occur in veins. The distribution of the secondary minerals in the basalt section shows both hydrothermal and oxidizing-nonoxidizing zonation. Most of the secondary minerals formed under alkaline, nonoxidizing conditions at temperatures up to 120° C. An acidic regime probably existed in the lowest portion of basalt. Oxidative diagenesis followed nonoxidative diagenesis in the upper part of the section. Oxidative diagenesis is characterized by the absence of celadonite, rare occurrences of dioctahedral smectite, and widespread hematite and phillipsite.

Carbonate minerals, uranium and thorium concentration and U-Th ages of sediments from ODP Leg 166 sites

We have performed U-Th isotope analyses on pure aragonite samples from the upper sections of Leg 166 cores to assign each aragonite-rich sediment package to the correct sea-level highstand. The uppermost sediment package from each of the four sites investigated (Sites 1003, 1005, 1006, and 1007) yielded a Holocene U-Th age. Sediment packages from deeper in the cores have suffered diagenesis. This diagenesis consists of significant U loss (up to 40%) in the site nearest the platform (Site 1005), slight U gain in sites further from the platform, and continuous loss of pure 234U caused by alpha recoil at all sites. The difference in diagenesis between the sites can be explained by the different fluid-flow histories they have experienced. Site 1005 is sufficiently close to the platform to have probably experienced a change in flow direction whenever the banks have flooded or become exposed. Other sites have probably experienced continuous flow into the sediment. Although diagenesis prevents assignment of accurate ages, it is sufficiently systematic that it can be corrected for and each aragonite-rich package assigned to a unique highstand interval. Site 1005 has sediment packages from highstands associated with marine isotope Stages 1, 5, 7, 9, and 11. Site 1006 is similar, except that the Stage 7 highstand is missing, at least in Hole 1006A. Site 1003 has sediment only from Stage 1 and 11 highstands within the U-Th age range. And Site 1007 has sediment only from the stage 1 highstand. This information will allow the construction of better age models for these sites. No high-aragonite sediments are seen for Stage 3 or Substages 5a and 5c. Unless rather unusual erosion has occurred, this indicates that the banks did not flood during these periods. If true, this would require the sea level for Substages 5a and 5c to have remained at least ~10 m lower than today.

Heavy minerals, grain size distribution, and ice-rafted debris in the Greenland Sea during 44 to 30 Ma

The widely accepted age estimate for the onset of glaciation in the Northern Hemisphere ranges between 2 and 15 million years ago (Ma). However, recent studies indicate the date for glacial onset may be significantly older. We report the presence of ice-rafted debris (IRD) in ~44 to 30 Ma sediments from the Greenland Sea, evidence for glaciation in the North Atlantic during the Middle Eocene to Early Oligocene. Detailed sedimentological evidence indicates that glaciers extended to sea level in the region, allowing icebergs to be produced. IRD may have been sourced from tidewater glaciers, small ice caps, and/or a continental ice sheet.